Field of the Invention
The present invention relates to a method of setting switching points in a system driven by a sensor configuration for any fixed ratio between the signal peaks in the output signal of a sensor.
The use of sensors to record the movement or the angular position of rotating parts is well known. Examples of this are crankshaft, camshaft, transmission, and ABS sensors in automobiles.
The sensors used in such cases are preferably Hall sensors, which sense the change in a magnetic field. For example, a permanent magnet is mounted on a part, which is in a fixed location, in order to produce a magnetic field. The magnetic field is then modulated by a gearwheel or other ferromagnetic pick-up, which is attached to the rotating part, according to position. In that configuration, the Hall sensor is preferably located between the permanent magnet and the gearwheel or pick-up, and is thus able to detect fluctuations in the magnetic field. If, for example, a tooth of the gearwheel is in the magnetic field, a "high" output signal is supplied, whereas a gap between the teeth produces a "low" output signal. In this way, the signal output by the Hall sensor can be used to infer the position or setting of a rotating part.
The signal supplied by a sensor is influenced considerably by the operating conditions under which the sensor is used. These operating conditions include unavoidable imponderablities, such as operating temperature or size of the air gap, etc. Despite the fluctuations caused by the operating conditions, the sensor should supply an output signal which is as well defined as possible. This means that the output signal should have a well defined waveform, irrespective of the fluctuations caused by the operating conditions. The reason for this is as follows:
If a sensor configuration supplies a sinusoidal signal, for example, then a well-defined response can be obtained from a system controlled by the sensor configuration if switching processes in the system, which depend on the output signal of the sensor, are carried out at the zero crossings of the signal. This is because these zero crossings are independent of the respective signal amplitude and, furthermore, have very steep edges.
Of course, in other signal waveforms of the output signal of the sensor, a switching point other than a zero crossing or the signal center may possibly also be advantageous.
Hence, when evaluating the output signal of a sensor for switching a system controlled by means of this sensor, a switching point should be maintained irrespective of the signal amplitude of the output signal of the sensor, and this applies even for very slow signals.
VDI Reports 1287, 1996, pages 583-611, "Eine neue Generation von `Hall-Effect`-Zahnradsensoren: Vorteile durch die Ver-bindung von BIMos Technologie und neuen Verpackungsrezepten" [A new generation of Hall-effect gearwheel sensors: advantages as a result of the combination of BIMos technology and new packing formulations], describes a sensor configuration in which the amplitude of the output signal of a sensor is initially normalized, possibly using an analog/digital (A/D) converter. Two further A/D and D/A converters are then used to record the signal peak values. From these, a switching threshold is then derived and defined. Finally, in this manner, it is possible to obtain a system response which is essentially independent of temperature fluctuations and the width of the air gap. That sensor configuration requires a relatively large outlay, however, since gain matching and numerous A/D converters are necessary.
German published patent application DE 32 01 811 A1 describes a device for recording rotational speed, angle, position and the like. In that configuration, the signal from a sensor is passed to switching means which monitor the amplitude and/or amplitude fluctuations. To do this, the amplitude is recorded by a peak value meter and passed to a threshold stage. This marks a permissible range for fluctuations in the signal amplitude. If the range is not adhered to, the signal from the sensor is switched off, which ensures that no distorted signals are output. According to that method, the signal output by the sensor is not corrected, i.e. there is no retrospective action by the threshold stage on the output signal, in other words the output signal is monitored only passively.